Gordon - I think they are anti reform because although they would be the majority party in a PR system, they would probably never again have a clear absolutely majority.
ATM the way the lefty vote is split between lib and lab, and the way the liberal vote is spread across the country, gives the Tories a v good chance of an outright majority.
PR would effectively stop that. That's my understanding of it, anyway.
Plus I think they are perhaps more ideologically attached to the constituency model anyway.